This application is related to Japanese application No. 2001-46197 filed on Feb. 22, 2001, whose priority is claimed under 35 USC xc2xa7 119, the disclosure of which is incorporated by reference in its entirety.
1. Field of the Invention
The present invention relates to a process of manufacturing a semiconductor device. More particularly, it relates to a process for solving a problem in that the polish rate (=polished amount/unit time) of an interlayer insulating film during chemical mechanical polishing is extremely high in a wafer periphery portion.
2. Description of Related Art
In accordance with integration at higher level and increase in capacity of integrated circuit devices, a wiring structure of semiconductor devices is getting to be miniaturized and multilayered. Accordingly, a process of forming an interwire insulating film or an interwire plug of greater flatness has been demanded. For obtaining such an interwire insulating film or an interwire plug of greater flatness, widely employed is a process of flattening an interlayer insulating film by chemical mechanical polishing (hereinafter abbreviated as CMP), forming connection holes by photolithography and dry etching, depositing metal such as tungsten to fill the connection holes and removing the metal on the interlayer insulating film by CMP.
It is generally known that a film to be polished, such as an interlayer insulating film or the like, is deposited at the deposition amount varying over the wafer surface. FIG. 4 shows the variation of the deposition amount among portions of the wafer surface, wherein A is a center portion, C is an edge portion and B is an intermediate portion between A and C. Type 1 shows a film deposited at the deposition amount decreasing from A to C, type 2 shows a film deposited at the deposition amount decreasing from A to B and increasing from B to C, type 3 shows a film deposited at the deposition amount increasing from A to C, and type 4 shows a film deposited at the deposition amount increasing from A to B and decreasing from B to C. The variation in deposition amount depends on the deposition rate.
As shown in FIG. 3, in the CMP step, a wafer periphery portion of about 1-2 mm width from a wafer edge is polished at the polish rate twice or more as great as that of a central portion ranging from a point of about 3 mm from the wafer edge to a wafer center. Accordingly, in polishing the film deposited at the deposition amount of type 1 or 4 shown in FIG. 4, there is a problem in that the film may excessively be polished at the wafer periphery portion.
FIGS. 6(a) to 6(d) are sections illustrating the steps of manufacturing a conventional semiconductor device. Referring to FIG. 6(a), a first insulating film 103 made of a BPSG film is formed by chemical vapor deposition (CVD) on a substrate 101 on which desired semiconductor devices are formed and the surface of the first insulating film is flattened by CMP. A lower wiring layer 104 is then formed on the first insulating film 103 and a second interlayer insulating film 105 made of a TEOS film is deposited thereon by CVD.
The first insulating film 103 is deposited at the deposition amount of type 2 or 3 mentioned above and is almost flattened by the following CMP.
The second interlayer insulating film 105 is deposited at the deposition amount of type 1 or 4. A thickness of the second interlayer insulating film 105 at a wafer edge 109 is smaller than that of the other portion.
Then, the second interlayer insulating film 105 is flattened by CMP as shown in FIG. 6(b).
Photolithography and dry etching are carried out to form a connection hole 106 and a conductive film 107 such as a tungsten film is deposited on the entire surface of the wafer by CVD as shown in FIG. 6(c). Before depositing the conductive film 107, a TiN/Ti layer (not shown) is formed by sputtering for improving the adhesion to the underlying layer.
Then, as shown in FIG. 6(d), the conductive film 107 on the second interlayer insulating film 105 is removed by CMP while leaving the conductive film 107 only in the connection hole 106, thereby forming a plug 108.
According to the process, the second interlayer insulating film 105 in the neighborhood of the wafer edge 109 is polished at an extremely high polish rate during CMP, thereby the thickness of the second interlayer insulating film 105 in the neighborhood of the wafer edge 109 is reduced as shown in FIG. 6(b).
On the other hand, FIGS. 7(a) and 7(b) show the steps of manufacturing another conventional semiconductor device. As shown in FIG. 7(a), a first interlayer insulating film 114 is deposited by CVD on a substrate 113 on which desired semiconductor devices are formed and then flattened by CMP. The first interlayer insulating film 114 is deposited at the deposition amount of type 1 or 4 shown in FIG. 4 and thus its thickness in the neighborhood of a wafer edge 115 is small.
Then, as shown in FIG. 7(b), the first interlayer insulating film 114 is flattened by CMP before forming a wiring layer.
According to the process, the first interlayer insulating film 114 has a small thickness in the neighborhood of the wafer edge 115 as shown in FIG. 7(a). Since the CMP is carried out at the polish rate extremely high in a wafer periphery portion of about 1-3 mm width from the wafer edge as shown in FIG. 2, the substrate 115 in the neighborhood of the wafer edge is also polished, which is not preferable.
As a solution for the extremely high polish rate in the neighborhood of the wafer edge, for example, Japanese Unexamined Patent Publication No. Hei 9 (1997)-139366 describes a technique for providing a retainer ring, a part of a wafer retaining member, with a rounded section at its circumference or an adjusted height to prevent extreme polishing in the wafer periphery portion, thereby maintaining an appropriate polish rate to obtain a flat surface.
However, even by the above technique, secondary deformation 122 in a polish cloth 121 contacting the neighborhood of a wafer edge 120 as shown in FIG. 8 is unavoidable, which causes a repulsion force 123 to the neighborhood of the wafer edge 120. Thus, it is impossible to inhibit the extremely high polish rate in the neighborhood of the wafer edge 120. In FIG. 8, reference numeral 124 denotes the retainer ring, 125 a wafer and 126 an insert pad.
In the step of forming the interwire plugs, the conductive film 107 is deposited on the second interlayer insulating film 105 as shown in FIG. 6(c) and then removed by CMP. However, since the second interlayer insulating film 105 has been polished at an extremely high polish rate in a wafer periphery portion 110, the conductive film 107 is not completely removed from the wafer periphery portion 110 and remains there as indicated by a reference numeral 111. Thus, an undesired object is left on the wafer.
On the other hand, in the step of forming the interlayer insulating film on a transistor, the substrate 113 itself is also polished during the flattening of the first interlayer insulating film 114 as shown in FIG. 7(b), which may generate an undesired object on the wafer.
In view of the above circumstances, the present invention provides a process of manufacturing a semiconductor device capable of preventing the generation of the undesired object after CMP.
According to the present invention, provided is a process of manufacturing a semiconductor device comprising the step of chemical mechanical polishing for flattening an interlayer insulating film deposited on a wafer on which desired elements are in advance formed, wherein a stopper layer is formed on a region which will be excessively polished through the chemical mechanical polishing before or after forming the interlayer insulating film.
According to the process of the present invention, the stopper layer is provided in advance on the region which will be excessively polished. Therefore, uniformity in thickness of the interlayer insulating film between the wafer periphery portion and other portion is improved, which allows the manufacture of a favorable semiconductor device.
Since the flatness of the interlayer insulating film improves, a wiring material to be filled in a connection hole for connecting wiring layers is prevented from remaining in a step difference portion in the wafer periphery portion.
It is preferred that the stopper layer has a thickness greater than an intended thickness of the interlayer insulating film to be obtained after the polishing by a thickness of the interlayer insulating film reduced by the polishing.
According to this feature, the stopper layer will not be removed from the region which will be excessively polished even after the polishing of the interlayer insulating film.
Further, it is preferred that the stopper layer has a width greater than a width greater than that of a resist layer to be removed from the wafer periphery portion in the photolithography step.
According to this feature, the excessive polishing in the wafer periphery portion is surely prevented.
Further, the stopper layer is preferably a silicon nitride film.
According to this feature, the interlayer insulating film made of an oxide film or the like is polished at a selective polish rate higher than that of the stopper layer.
These and other objects of the present application will become more readily apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.